The present invention relates to apparatus with a rotary head for recording and playing back digital audio signals or other digital information signals.
Video-tape recorders (VTRs) with a rotary head for recording high definition television signals (hereinafter referred to as HDTV signals), by forming helical tracks on a magnetic tape, and playing back the recorded signals have been developed.
For instance, an article "Wideband Recording Technology for High-definition Baseband VCRs," in IEEE Transactions on Consumer Electronics, Vol. CE-33, No. 3, August 1987 shows a VTR for recording HDTV signals in one field, being divided into 3 segments each consisting of 2 channels.
The drum and head configuration of this VTR is shown in FIG. 29, and its track pattern is shown in FIG. 30.
As illustrated, a magnetic tape 104 moving in the direction of an arrow 106 is passed around a rotary drum 101 rotating in the direction indicated by an arrow 105. A pair of heads 102a and 102b are disposed adjacent to each other and serve as channels A and B (hereinafter referred to as CH.A and CH.B), anti another pair of heads 103a and 103b adjacent to each other are disposed 180.degree. spaced apart from the heads 102a and 102b to serve as a pair of channels. The magnetic heads mounted on the periphery of the rotary drum 101 scan the magnetic tape 104 in the direction indicated by an arrow 107 (FIG. 30). During recording, such scanning form tracks 108, each of which is formed by one scanning by a head for one channel. A video signal of one field is recorded over an area T which comprises several tracks.
A pair of tracks CH.A and CH.B formed by the pair of heads are called a segment. A video signal of one field is therefore recorded in three segments.
The VTR recording HDTV signals records signals of a frequency band wider than the conventional TV signals. The following methods are therefore employed.
(1) The HDTV video signals are divided into two channels in order to reduce the frequency band per channel. PA0 (2) The rotational speed of the drum is increased to 90 rps (revolution per second) which is three times higher than in the conventional VTR to increase the relative speed between the tape and the head to accomplish a wide band FM (frequency-modulated) recording. As a result, the video signal in one field is recorded being divided into three segments.
Since the actual format of the video signal recorded is not relevant to the invention, its description is omitted.
As has been described, a scheme widely adopted in recording and playing back HDTV signals is to divide the video signal of one field or one frame into a plurality of segments each consisting of a plurality of channels.
When an audio signal corresponding to the HDTV signal is recorded, it is desirable to record and play back in digital form, employing PCM (pulse-coded modulation) for example, in order to achieve a high quality audio signal.
In the VTRs described above, when a digital audio signal is to be recorded in addition to the video, for the purpose of facilitating independent rewriting of the video and the audio (after-recording), it is contemplated to dispose a region for digital audio recording on the extension of the video tracks, as in an 8 mm VTR.
An attempt along this line is shown in the article "Wideband Compression Hi Vision VTR," National Technical Report, Vol. 32, No. 4, August, 1986.
FIG. 31 is a schematic diagram showing the track patterns recorded by such a device. As illustrated, a video signal of one field is divided into 2 channels, A and B, and recorded in a single segment. The signal area for the video signal on one track is denoted by 109. The audio signal of the two channels in the one field is recorded in the digital audio signal areas 110 formed in each track, being separated from the video signal areas by a gap or a predetermined length. The audio signal of one channel is recorded in association with the area for the video signal for one channel, CH.A, and the audio signal of the other channel is recorded in association with the area for the video signal of the other channel, CH.B.
In the conventional apparatus having rotary heads for recording and playing back the digital audio signals and the like, when one head is not functioning, the audio information of one channel of one field is entirely lost.
Another problem is that the recording system does not have sufficient error correcting or error compensating capability against burst errors due to an extended scratch on the tape.